The 2012 champion at Augusta National sparked the best run of the tournament so far when he stuck his tee shot at No. 12 within 3 feet of the cup. He tapped in for the first of five straight birdies that propelled him to a 4-under 68.

Even after making his second bogey of the tournament by missing a short putt at the 18th, Watson walked off with his second straight round in the 60s, a 7-under 137 total and a three-stroke lead — the biggest 36-hole advantage at Augusta since 2006.

"It's not science here," Watson said. "It's try to hit the greens, and if you're hitting the greens that means you're obviously hitting your tee shots well. So that's all I'm trying to do, just hit the greens."

Look who's in the mix again, too: 54-year-old Fred Couples, who posted his second straight 71.

This is the fifth straight year the 1992 winner has gone to the weekend in the top 10 — he was leading two years ago — but he's never been able to hang on.

"I can't panic," said Couples, looking to become the oldest major champion in golf history. "You're not going to pick up two or three shots here because you want to. It's not that kind of course. You've got to hang in there, expect a tough shot here and there. It's going to be a tough day tomorrow."

And don't count out defending champion Adam Scott, who got off to a rough start but rallied for 72. The Aussie was among those four shots back, still solidly in contention to become only the fourth back-to-back winner in Masters history.

Watson opened Thursday with a 69 and went bogey-free through the first 26 holes, finally stumbling at the ninth. But that bogey was quickly forgotten when he put on a dazzling display of the golf that had the patrons roaring. He took advantage of both par 5s, sandwiched around a curling, 40-foot birdie putt at the 14th that prompted him to throw both arms in the air.

Watson made it five in a row at the par-3 16th, pulling off another magnificent tee shot with the 9-iron, the ball rolling up about 4 feet short of the flag. He became only the fifth player in Masters history to run off nothing but birdies from the 12th to 16th holes.

A year ago, the left-hander finished in a tie for 50th last year as the defending Masters champion, his worst showing in five previous appearances. He likes being two years removed from his title a whole lot better.

"I was in awe when I was the champion," Watson said. "I didn't know how to handle it the best way, so I didn't play my best golf."

Watson's closest pursuer was Australia's John Senden, who birdied 14 and 15 on his way to a 68 and 140 overall.

Graham DeLaet of Weyburn, Sask., shot an even-par second round, but his disappointing first round of 8 over will see him cut from the final weekend. The project cut is 4 over.

Former Masters champion Mike Weir of Bright's Grove, Ont., will almost assuredly move on after a round of even par. He followed four birdies on the front nine with four bogeys on the back to sit at 1 over after two rounds.

Scott bogeyed three of the first five holes but wound up at 141. He was joined by Denmark's Thomas Bjorn, who birdied four of the last five holes for a 68; Sweden's Jonas Blixt, who managed 71 despite a double-bogey at the 11th; and 20-year-old Jordan Spieth, hardly looking like an Augusta rookie when he closed out 70 with a birdie at the tough finishing hole.

Five shots back with Couples were Jimmy Walker, a three-time PGA Tour winner this season who shot 72, and Jim Furyk, whose 68 matched Watson, Senden and Bjorn for the best round of the day.

First-round leader Bill Haas, teeing off on a warm, sunny afternoon with the wind picking up and the greens getting firmer, was still at 4 under approaching the turn. Then came a miserable stretch of holes starting at No. 9: bogey, bogey, double-bogey, bogey, bogey. He staggered to a 78 — 10 shots higher than the day before, knocking him nine shots back.

At least Haas gets to keep playing.

Three-time winner Phil Mickelson missed the Augusta cut for the first time since 1997.

Lefty had a triple-bogey at the 12th, where he knocked three straight shots in bunkers for his second triple of the tournament. Three birdies on the back side gave him a glimmer of hope, but 73 totalled up to 149 — one shot too many.

"It's tough to overcome those big numbers," said Mickelson, who had plenty of big-name company beyond the cut line.

Sergio Garcia, Luke Donald, Ernie Els, Graeme McDowell, Dustin Johnson, Angel Cabrera and Charl Schwartzel were all headed home as well before the weekend.